Respiratory illness from RSV infection can be life threatening for children with underlying lung disease or CHD. Palivizumab (MEDI-493, Synagis TM) is a humanized monoclonal IgG1 which has been shown to reduce the incidence of RSV-associated hospitalizations in children with underlying lung disease. A double-blind placebo-controlled, randomized multi-center study will be undertaken to assess the safety of palivizumab in children with CHD.